Thermostat contact having a dual annular inwardly sloped contacting surface thereon



June 15, 1965 P. R. LEE 3,189,721

THERMOSTAT CONTACT HAVING A DUAL ANNULAR INWARDLY SLQPED CONTACTING SURFACE THEREON Filed April 12, 1963 2 Sheets-Sheet 1 2\ I9 20 ,1 Fig.2. i B 10111 l8 ZI/ ///1 ':/1' E Fig. 4.

wn'usssss I lNVENT OR Ilium Paul R. Lee

ATTORNEY June 15, 1965 P..R. LEE 3,189,721

. THERMOSTAT CONEHGT HAVING A DUAL ANNULAR INWARDL SLOPED] (IQNTACT'ING SURFACE THEREON Filed Ap ril 12;; 1963 2 Sheets-Sheet 2 United States Patent 3,189,721 THERMUSTAT CONTACT HAVING A DUAL AN- NULAR IIJWARDLY SLGPED CGNTACTING SURFACE THEREON Paul R. Lee, Mansfield, (lhio, assignor to Westinghouse Electric Corporation, Pittsburgh, 1 21., a corporation of Pennsylvania Filed Apr. 12, 1963, Ser. No. 272,700 7 Claims. (Cl. Nil-466) This invention relates to thermostat contacts and, more particularly, to contacts to be used in a thermostat of the slow action type. i

In thermostatic devices of the slow make and break type which may, for example, be employed in range switches and drier controls, there often exists a problem referred to as contact flutter. By contact flutter is meant a condition where a single are at the contacts occurs for more than a quarter of a second. This condition frequently occurs on new contacts and generally is eliminated after the contacts has cycled several hundred times.

However, before this undesirable arcing condition is improved by the contacts being cycled in use, the contacts may be adversely effected. Some ill effects of arcing are serious erosion of the contact surfaces, a shift in temperature calibration of the device, and high localized tempera tures at the contacts resulting in partial anneal of the contacts.

It is, therefore, an object of the invention to lessen contact flutter in a thermostatic device.

A further object of the invention is to provide a pair of contacts for use in a thermostatic device, which contacts do not display undesirable arcing during the entire operation of the device.

These objects, and other objects which will become apparent as the description proceeds, are achieved by providing a pair of contacts, one having a relatively planar surface and the mating contact having a novel contact area. This novel contact area comprises outer annular surface area sloping toward the plane of the first contact at a prescribed angle. Adjacent the inner portion of this annular area is an inner area having its innermost portion disposed to contact the planar surface of the first contact. The inner surface is sloped at a slightly different angle than that of the outer surface such that in the closed contact position, the inner surface forms a smaller angle with the mating contact surface than does the outer surface.

For a better understanding of the invention, reference should be had to the accompanying drawings, wherein:

FIGURE 1 is a schematic view of a flasher control having the invention employed therein;

FIG. 2 is an elevational view showing a portion of the control shown in FIG. 1, on a larger scale;

FIG. 3 is a bottom plan view of the upper contact of FIG. 2 showing in detail the contact surfaces;

FIG. 4 is an elevational view similar to FIG. 2 but showing an alternate embodiment of the invention;

FIG. 5 is a bottom plan view of the upper contact of FIG. 4 showing in detail the contact surfaces of the alternate embodiment;

FIG. 6 is an elevational view similar to FIG. 2 but showing another embodiment of the invention;

FIG. 7 is a bottom plan view of the upper contact of FIG. 6 showing in detail the contact surfaces of that embodiment;

FIG. 8 is an elevational view similar to FIG. 2 but showing still another embodiment of the invention; and

FIG. 9 is a bottom plan view of the upper contact of FIG. 8 showing in detail the contact surfaces of that embodiment.

Although the principles of the invention are broadly ap- ICC plicable to thermostat contacts, the invention is herein illustrated in connection with a flashing control for a surface heater.

Referring to the drawings, especially FIG. 1, there is shown schematically apparatus for flashing a surface heater 1% of an electric range or the like, the apparatus including a wattage control 11 and a circuit transfer mechanism 12 preferably disposed at opposite sides of the heater 10 and in series therewith in an electrical circuit from the conductor L1 to either line conductor L2 or neutral line conductor N.

The voltage control 11 includes a pair of cooperating contacts 15 and 17, which, when in engagement, close the electrical circuit to the main heater 1%.

The control illustrated in FIG. 1 forms no part of the present invention, but is shown merely to illustrate one type of apparatus in which the present invention is useful, this invention being incorporated in the cooperating contacts 15 and 17.

If a more detailed description of the control of FIG. 1 is desired, reference should be made to US. Patent No. 2,993,976 granted July 25, 1961 to applicants assignee.

Referring now to FIG. 2, the contact 17 is shown to have a planar surface 18, facing the cooperating contact 15. The contact 15 is circular, as best shown in FIG. 3, and has the downwardly facing surfaces 19 and 20* disposed in facing relationship with the surface 18 of the contact 17. Both the outer annular surface 19 and the inner circular surface 2b are sloped toward the planar surface 18 of the contact 17, the surface 20 being bounded by the inner circumference of the surface 19. With the contacts 15 and 17 in the closed position as shown by the dotted lines in FIG. 2, the surface 19 forms the angle designated as A with the surface 18 of the contact 17, and the surface 2t forms the angle designated as B with the surface 18. The surface 19 and the surface 26 are constructed such that the angle B is always slightly less than the angle A.

By way of example, angle A may be in the range of from 10 to 20 while the angle B should be less than 8. On contacts wherein the outer portion of surface 19 has a diameter greater than inch, the inner portion 21 of the surface 20 may have a radius of inch or less formed thereon.

In FIGS. 4 and 5, there is shown a second embodiment having a contact 17 and cooperating contact 15a. The contact 17 is similar to the contact 17 shown in FIG. 2 having a contact surface 18 which is a planar surface. The contact 15a comprises an outer annular surface 22 and an intermediate annular surface 23. The surface 22 slopes inwardly toward the surface 18 of the contact 17 forming an angle C, therewith and the surface 23 slopes inwardly toward the surface 18 forming the angle D therewith and the angle D is slightly less than the angle C. In addition, there is an inner circular surface 24 adjacent the inner portion of the surface 23 and sloping inwardly away from the surface 18 of the contact 17 at an angle E thereto. When the contact 15a and the contact 17 are in the closed position as shown by the dotted lines of FIG. 4, the annular knife edge 25 formed at the intersection of the surfaces 23 and 24, contacts the surface 18.

Satisfactory results may be achieved by having angle C in the range of from 10 to 20 while angle D is less than 8. Angle E may be the same as the angle D.

During the initial use of the contact 15 or the contact 15a, engagement of these contacts with the contacts 17 is confined to the inner portion 21 of the contact 15 or the annular edge 25 of the contact 15a. During operation, the mating surface of contact becomes greater as the inner portion 21 or the annular edge 25 wears down. However, during the cycling necessary to wear the inner portion 21 or the edge 25, contact flutter is lessened or 3 eliminated, and the contacts do not display an undesirable arcing characteristic.

In FIGS. 6 through 8 are shown two embodiments of the invention wherein the sloping surfaces of one of the contacts are arcuate surfaces.

Referring to FIGS. 6 and 7, there is shown a contact 15b cooperating with a contact 17 which is similar to the contact 17 of FIGS. 2 through 5. The contact 15b has an outer surface 34B developed by rotation of an are having a radius R emanating from the contact centerline 32, about the centerline. An inner surface 32 is likewise developed by the rotation of an are having a radius R emanating from the centerline 32, about the centerline.

It should be noted that the contact 15b is similar to the contact 15 but for the curved sloping surfaces 3'3 and 32 replacing the straight sloping surfaces 19 and 2%, respectively.

FIGS. 8 and 9 shows a contact 15c together with a mating contact 17 similar to the mating contact 1? of the previously described embodiments. The contact 150 has an outer surface 33 developed by the rotation of an are having a radius R, emanating from the contact centerline 34, about the centerline. Similarly, an are having a radius of R is revolved about the centerline to develop the curved surface 35. The surfaces 33 and 3d of the contact 15c are similar to the surface 22 and the surfaces 23 and 24 respectively of the contact 15a, but with curved sloping surfaces of the contact 150 replacing the straight sloping surfaces of the contact 150.

Satisfactory results may be accomplished in contacts having an outer diameter of /2 inch or greater by providing R in the area of A to 1 inch with R greater than 7 inch when the contact 15b is use In /s inch diameter contacts having the configuration of 15c, R should be in the area of 3 inch to 5 inch with R greater than inch.

It is believed that one reason the contact construction herein disclosed solves the flutter problem is that the relatively large angle A of FIG, 2 and C of FIG. 4, by materially increasing the distance between the contacts 15 and 17 at their peripheries, when they are engaged, helps to cool the arc and give it room to extinguish itself.

While the invention has been shown in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of further changes and modifications without departing from the spirit thereof.

What is claimed is:

1. In an electrical control, a pair of cooperating contacts one of said contacts having a planar contact surface the contact surface of the other of said contacts comprising an outer annular surface sloped inwardly toward said planar surface,

and an inner surface disposed adjacent the inner circumference of said outer surface and sloped inwardly toward said planar surface,

said outer surface forming an angle with said planar surface which is greater than the angle formed by said inner surface and said planar surface,

and the inner portion of said inner surface contacting said planar surface when said pair of contacts are in the closed position.

2. The structure of claim 1 wherein the outer diameter of said outer annular surface is greater than one eighth inch and the angle formed between said inner surface and said planar surface is less than eight degrees.

3. In an electrical control, a pair of cooperating contacts one of said contacts having a planar contact surface the contact surface of the other of said contacts comprising an outer annular surface sloped inwardly toward said planar surface,

and an inner surface disposed adjacent the inner circumference of said outer surface and sloped inwardly toward said planar surface said outer surface forming an angle in the range of from ten to twenty degrees with said planar surface, said inner surface forming an angle of less than eight degrees with said planar surface,

and the inner portion of said inner surface contacting said planar surface when said pair of contacts are in the closed position.

4. In an electrical circuit, a pair of cooperating contacts,

one of said contacts having a planar contact surface,

the contact surface of the other of said contacts comprising an outer annular surface sloped inwardly toward said planar surface,

an inner annular surface disposed adjacent the inner circumference of said outer surface and sloped inwardly toward said planar surface,

and an inner circular surface adjacent the inner portion of said inner annular surface and sloped inwardly from said planar surface, said outer surface forming an angle with said planar surface which is greater than the angle formed by said inner annular surface and said planar surface,

and the inner portion of said inner annular surface contacting said planar surface when said pair of contacts are in the closed position.

5. The structure of claim 4 wherein said angle formed by said one inner surface and said planar surface is substantially equal to the angle formed by said other inner surface and said planar surface.

6. In a thermostatic control, a pair of cooperating contacts,

the first of said contacts having a planar contact surface, the second of said contacts comprising an outer annular surface sloped inwardly toward said planar surface,

an inner annular surface disposed adjacent the inner circumference of said outer surface and sloped inwardly toward said planar surface,

and an inner circular surface adjacent the inner portion of said inner annular surface and sloped inwardly from said planar surface,

said outer surface forming an angle in the range of from ten to twenty degrees with said planar surface,

said one inner circular surface forming an angle of less than eight degrees with said planar surface,

and The inner portion of said one inner surface when said pair of contacts are in the closed position thereby closing an electric circuit.

'7. The structure of claim 6 wherein said angle formed by said one inner surface and said planar surface is substantially equal to the angle formed by said other inner surface and said planar surface.

No references cited.

BERNARD A. GILHEANY, Primary Examiner. 

1. IN AN ELECTRICAL CONTROL, A PAIR OF COOPERATING CONTACTS ONE OF SAID CONTACTS HAVING A PLANAR CONTACT SURFACE THE CONTACT SURFACE OF THE OTHER OF SAID CONTACTS COMPRISING AN OUTER ANNULAR SURFACE SLOPED INWARDLY TOWARD SAID PLANAR SURFACE, AND AN INNER SURFACE DISPOSED ADJACENT THE INNER CIRCUMFERENCE OF SAID OUTER SURFACE AND SLOPED INWARDLY TOWARD SAID PLANAR SURFACE, SAID OUTER SURFACE IS FORMING AN ANGLE WITH SAID PLANAR SURFACE WHICH IS GREATER THAN THE ANGLE FORMED BY SAID INNER SURFACE AND SAID PLANAR SURFACE, AND THE INNER PORTION OF SAID INNER SURFACE CONTACTING SAID PLANAR SURFACE WHEN SAID PAIR OF CONTACTS ARE IN A CLOSED POSITION. 